1. Field of the Invention
The invention relates generally to tools for preparing a hole to receive an implant or fixture, and more particularly to rotary osteotomes and methods implemented thereby for expanding an osteotomy or hole in cellular material to receive an implant or other fixation device.
2. Description of Related Art
An implant is a medical device manufactured to replace a missing biological structure, to support a damaged biological structure, or to enhance an existing biological structure. Bone implants are implants of the type placed into the bone of a patient. Bone implants may be found throughout the human skeletal system, including dental implants in a jaw bone to replace a lost or damaged tooth, joint implants to replace a damaged joints such as hips and knees, and reinforcement implants installed to repair fractures and remediate other deficiencies, to name but a few. The placement of an implant often requires a preparation into the bone using either hand osteotomes or precision drills with highly regulated speed to prevent burning or pressure necrosis of the bone. After a variable amount of time to allow the bone to grow on to the surface of the implant (or in some cases to a fixture portion of an implant), sufficient healing will enable a patient to start rehabilitation therapy or return to normal use or perhaps the placement of a restoration or other attachment feature.
In the example of a dental implant, preparation of a hole or osteotomy is required to receive a bone implant. According to current techniques, at edentulous (without teeth) jaw sites that need expansion, a pilot hole is bored into the recipient bone to form the initial osteotomy, taking care to avoid the vital structures. The pilot hole is then expanded using progressively wider expander devices called osteotomes, manually advanced by the surgeon (typically between three and seven successive expanding steps, depending on implant width and length). Once the receiving hole has been properly prepared, a fixture screw (usually self-tapping) is screwed into place at a precise torque so as not to overload the surrounding bone.
The osteotome technique has become widely utilized in certain situations requiring preparation of an osteotomy site by expansion of a pilot hole. By nature, the osteotome technique is a traumatic procedure. Osteotomes are traditionally not rotating devices but rather advanced with the impact of a surgical mallet, which compacts and expands the bone in the process of preparing osteotomy sites that will allow implant placement. Treatment of a mandibular site, for example, is often limited due to the increased density and reduced plasticity exhibited by the bone in this region. Other non-dental bone implant sites may have similar challenging density and plasticity characteristics. Or, the location of the bone may be wholly unsuitable for the violent impact of an osteotome, such as in small bone applications like the vertebrae and hand/wrist areas to name a few. Additionally, since the traditional osteotome is inserted by hammering, the explosive nature of the percussive force provides limited control over the expansion process, which often leads to unintentional displacement or fracture such as in the labial plate of bone in dental applications. Many patients do not tolerate the osteotome technique well, frequently complaining about the impact from the surgical mallet. In addition, reports have documented the development of a variety of complications that result from the percussive trauma in dental applications, including vertigo and the eyes may show nystagmus (i.e., constant involuntary cyclical movement of the eyeball in any direction).
More recently, alternative techniques to the hammered osteotome have been developed for bone applications that allow for less traumatic preparation of implant sites. These alternative procedures are based on the use of motor-driven screw-type bone expanders, such as those marketed by Meisinger (Neuss, Germany). First a pilot hole is drilled at the implant site, then a series of progressively larger expander screw taps are introduced into the bone by hand or with motor-driven rotation, which decreases surgical trauma (as compared with hammer taps) while providing some degree of control over the expansion site. The thread pattern of the expander screw taps is intended to compact bone laterally as the expander tap advances into the osseous crest. This system allows expansion and preparation of implant sites in Type II and III bone, as well as compaction of Type IV bone.
US Publication No. 2006/0121415 to Anitua Aldecoa describes the use of motor-driven tools and methods for expanding a human bone for the purpose of installing a dental implant. Similar to the progressive illustration described above, a starter drill is used to create a pilot hole followed by the insertion of an expander screw tap type osteotome having a conical/cylindrical geometry with progressive cross-section. A surgical motor is used to rotate the osteotome at relatively low speeds. Another example of this technique is described in U.S. Pat. No. 7,241,144 to Nilo et al, issued Jul. 10, 2007. The entire disclosures of US Publication No. 2006/0121415 and U.S. Pat. No. 7,241,144 are hereby incorporated by reference.
U.S. Pat. No. 7,402,040 to Turri, issued Jul. 22, 2008, discloses a hybrid hammered and rotary osteotome technique using a non-circular osteotome design. In the preferred embodiment, the non-circular osteotome is first hammered to the bottom of the osteotomy, and then when at full depth rotated back-and-forth by hand to achieve a final expansion shape. In an alternative embodiment however, impulse hammering and rotation are concurrently applied in order to drive the osteotome deeper into the osteotomy, which advance into the osteotomy is encouraged by helical edges that generate “a tractive force that tends to advance it [the osteotome] towards the interior of the osseous site”. (Turri at Column 9, lines 42-43.) In other words, Turri's alternative embodiment osteotome uses screw threads in combination with percussive hammering and powered rotation to pull the osteotome down into the osteotomy.
In the prior art designs involving motor-driven bone expansion, including those of Anitua Aldecoa, Niro and Turri described above, the rotary speed of the expander screw tap is locked in a fixed relationship to the expansion rate of the osteotomy. This is because threads on the expander device cut into the bone and “pull” the expander tap deeper into the initial osteotomy with rotation. Axial advance is thus controlled by pitch of threads and rotation speed; the thread pitch of the expander is fixed and cannot be altered on-the-fly by the surgeon. If a surgeon wishes to expand the bone more slowly, the only recourse is to turn the expander more slowly. Conversely, if the surgeon wishes to expand the bone more rapidly, the only option is to turn the expander tool more quickly. Thus, the rate of bone expansion is a direct and unalterable function of the rate at which the surgeon turns the expander tool, and the surgeon is unable to vary other parameters such as pressure and/or rotation rate to achieve an optimum expansion rate.
This inexorable linking of tool rotation rate to bone expansion rate in all prior art rotary expander systems limits surgical control over the implant process, and in some cases may lead to unnecessary patient discomfort. There is therefore a need in the art for an improved surgical method for expanding an osteotomy to receive an implant in all bone applications, and tools therefor, that provide greater surgical control, are less costly, less likely to introduce error and that reduce patient discomfort.
Another area of interest with respect to preparing bone to receive an implant or fixation screw is the subsequent osseointegration of the implant. The direct structural and functional connection between living bone and the surface of a load-bearing artificial implant leads to enhanced overall success of the surgical procedure for the patient. Current approaches to improving the direct contact of bone and implant surface are directed toward the use of engineered cements and/or proprietary implant surfaces that typically include porous construction. The porous properties of the implant surface contribute to extensive bone infiltration, allowing osteoblast activity to take place. In addition, the porous structure allows for soft tissue adherence and vascularization within the implant. One significant disadvantage of the current approaches to improving osseointegration, namely the use of cements and implant constructions, is the relatively high added cost. The cements and engineered implants tend to be proprietary products marketed at premium prices. For example, it is not uncommon for a single bone screw used in a standard fixation application to cost $5000 (USD).
There is therefore a need for improved tools and techniques that facilitate osseointegration without the attendant high cost associated with present cements and engineered implants.
Furthermore, other types of non-organic cellular materials, such as metal foams used in some aerospace applications, also require fixation techniques that may benefit from the hole preparation concepts used in the medical field for preparing bone.